The researchers used data from 2006 to 2008 from the National Survey on Drug Use and Health, an annual study representative of the U.S. population, to study 18- to 25-year-olds’ drug use behavior. They found that 12 percent of the survey population reported misusing prescription opioids around the time the survey was conducted.

They also found that both men and women who had smoked marijuana between the ages of 12 and 17 were more than two times more likely to later abuse prescription drugs than those who had not. Young men who drank or smoked cigarettes as teens were 25 percent more likely to abuse prescription drugs — though this link was not found in women surveyed. Fiellin said there was no clear-cut reason why the results differed for men and women.

Keith Humphreys, professor of psychiatry at the Stanford Medical Center, said that this association between “gateway drugs” and prescription pain medication was significant regardless of the exact mechanism behind the link.

“Some people believe the ‘gateway effect’ exists because early drug use primes the human brain for more drug-seeking, others argue that the friends you make using drugs as a youth are a ready source for other drugs later, and still others argue that there are factors, like impulsivity, that causes both early and later drug use,” Humphreys said. “Which camp is correct? Probably, all of them.”